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Spatial ecology of a wastewater network defines the antibiotic resistance genes in downstream receiving waters

Lookup NU author(s): Marcos Quintela-Baluja, Dr Yongjie Yu, Professor David Graham



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


© 2019 The Authors. Wastewater treatment plants (WWTPs) are an effective barrier in the protection of human and environment health around the world, although WWTPs also are suggested to be selectors and-or reservoirs of antibiotic resistance genes (ARGs) before entering the environment. The dogma about WWTPs as “ARG selectors” presumes that biotreatment compartments (e.g., activated sludge; AS) are single densely populated ecosystems with elevated horizontal gene transfer. However, recent work has suggested WWTP biotreatment compartments may be different than previously believed relative to antibiotic resistance (AR) fate, and other process factors, such as bacterial separation and specific waste sources, may be key to ARGs released to the environment. Here we combined 16S rRNA metagenomic sequencing and high-throughput qPCR to characterise microbial communities and ARGs across a wastewater network in Spain that includes both community (i.e., non-clinical urban) and hospital sources. Contrary to expectations, ARGs found in downstream receiving waters were not dominated by AS biosolids (RAS), but more resembled raw wastewater sources. In fact, ARGs and microbial communities in liquid-phase WWTP effluents and RAS were significantly different (Bray–Curtis dissimilarity index = 0.66 ± 0.11), with a consequential fraction of influent ARGs and organisms passing directly through the WWTP with limited association with RAS. Instead, ARGs and organisms in the RAS may be more defined by biosolids separation and biophysical traits, such as flocculation, rather than ARG carriage. This explains why RAS has significantly lower ARG richness (47 ± 4 ARGs) than liquid-phase effluents (104 ± 5 ARGs), and downstream water column (135 ± 4 ARGs) and river sediments (120 ± 5 ARGs) (Tukey's test, p < 0.001). These data suggest RAS and liquid-phase WWTP effluents may reflect two parallel ecosystems with potentially limited ARG exchange. As such, ARG mitigation in WWTPs should more focus on removing bacterial hosts from the liquid phase, AR source reduction, and possibly disinfection to reduce ARG releases to the environment.

Publication metadata

Author(s): Quintela-Baluja M, Abouelnaga M, Romalde J, Su J-Q, Yu Y, Gomez-Lopez M, Smets B, Zhu Y-G, Graham DW

Publication type: Article

Publication status: Published

Journal: Water Research

Year: 2019

Volume: 162

Pages: 347-357

Print publication date: 01/10/2019

Online publication date: 01/07/2019

Acceptance date: 30/06/2019

Date deposited: 15/07/2019

ISSN (print): 0043-1354

ISSN (electronic): 1879-2448

Publisher: Elsevier Ltd


DOI: 10.1016/j.watres.2019.06.075


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Funder referenceFunder name
MR/P028195/1Medical Research Council (MRC)